Adjustable leg safety ladders



July 12, 1966 T. K. ZEVELY 3,260,329

ADJUSTABLE LEG SAFETY LADDERS Filed Aug. 1'7, 1964 F1G.4.. FIG. 5.

INVENTOR THOMAS K. ZEVELY C a/rrW gK WH MW ATTORNEYS United States Patent f 3,260,329 ADJUSTABLE LEG SAFETY LADDERS Thomas K. Zevely, College Park, Md., assiguor to Camphell Sand (10., Inc, College Park, Md, a corporation of Maryland Filed Aug. 17, 1964, Ser. No. 389,882 7 Claims. (Cl. 182-202) The present invention relates to safety ladders, and, more particularly, to stepladders having adjustable leg extensions.

Oftentimes ladders are required to be used under conditions where the supporting surface, upon which the ladder is intended to be set, may vary considerably in evenness, thus imparting a dangerous lateral tilt to the ladder Which may cause the user to be inadvertently dislodged therefrom with resultant injuries.

Accordingly, it is a principal object of the present invention to provide a ladder having a pair of interconnected, adjustable leg extensions and novel locking means therefor which, in combination with the other elements of a conventional folding stepladder, enable the steps thereof to be maintained substantially horizontal when in use on supporting surfaces of irregular or uneven character.

Another principal object of the invention is to provide a ladder of the aforementioned character wherein the novel locking means is efiiciently and automatically operative in response to the application of the users weight upon any one of the steps of the ladder, remaining locked as long as the application of weight continues to exist thereon.

Still another object is to provide an improved ladder according to the preceding objectives wherein yieldable means are included in association with the locking means to automatically unlock or release the adjustable legs from their locked condition upon removal or withdrawal of the users weight from said ladder, whereby said legs may be returned to a normally equalized condition.

The objectives and advantages of my improved safety ladder are achieved by utilizing, in combination with a generally conventional foldable-type stepladder, a pair of spaced-apart equalizing extension legs which are telescopically housed or mounted within a pair of rear prop leg-s, and connected by an arcuate mounting plate which is pivotally supported between said rear prop legs. Locking means, which include a plurality of locking teeth on the arcuate plate and a complemental, shiftable, locking detent or dog whichis operable by means of a novel bell crank and lever arrangement disposed within the front legs of the ladder, serve to lock the extensible equalizing legs in any of a given range of adjustable positions responsive to the application of the users weight upon any of the steps of the ladder. Said locking means are yieldably mounted for automatic releasing or unlocking thereof by retraction of the locking dog from engagement with said teeth when the user removes his body weight from the ladder, whereby the extensible legs may be normally equalized for storage or are free to be adjusted to a new position as desired.

The foregoing and other objects and advantages of the invention will appear more fully and will become more apparent upon consideration of the following detailed description taken in conjunction with the accompanying drawings. In this connection, while one specific embodiment of the inventive concept is described and illustrated, it is to be expressly understood that the drawings are illustrative only and not to be construed as representative of the full scope of the invention as it is defined in the ap pended claims.

Referring now to the drawings, wherein like reference characters designate like parts throughout the several figures:

FIG. 1 is a three-quarter perspective view from the 3,26%,329 Patented July 112, 1966 front and below of a relatively short stepladder embodying the invention;

FIG. 2 is a rear elevational view, with a small portion of one leg broken away, of the improved ladder of FIG. 1, with the leg extensions in an equalized and balanced condition;

FIG. 3 is a view similar to FIG. 2 but depicting the leg extensions in an unbalanced or shifted condition; and

FIG. 4 is an enlarged transverse cross-sectional view of the ladder taken substantially on line 4-4 of FIG. 3, and better showing the structural details thereof.

Referring now to the drawing figures, my improved safety ladder, designated generally at 10, includes a conventional pair of front legs 12 and 14 which serve as side rails for a plurality of conventional steps 16 suitably affixed therebetween, and a top platform 18 to which said front legs are angularly affixed at their upper extremities.

A pair of spaced-apart rear prop legs 20 and 22, which are substantially shorter than the front legs as designated at their respective lower extremities 24 and 26, have their upper extremities conventionally pivotally attached as at 28 to the upper platform 18 adjacent the connections of the front legs thereto, and, when opened for use, are disposed angularly away from said front legs, being braced by conventional foldable bracing links designated 30.

The legs of the ladder .are preferably constructed of a lightweight, channel formed material, such as aluminum or magnesium or alloys thereof, which readily lends itself to housing the leg extensions and a portion of the lock actuating linkage as described below.

The adjustability feature, as illustrated, includes a pair of elongated leg extension members 32 and 34 which are of a size to readily slide or telescopically shift in a generally vertical manner within rear prop legs 20 and 22, being retained therein by keeper straps 36 at the lower ends of legs 20 and 22. The upper ends of the extensible legs 32 and 34 are preferably bifurcated as at 38 or otherwise formed to provide pivotal connections 40 to opposite sides of a semicircular equalizing plate 42. The plate 42 is pivotally mounted at 44, below the top platform 18 and mid-way between pivots 40, 40, to a cross brace 46 which interconnects the upper intermediate areas of rear prop legs 20 and 22. The leg extensions 32 and 34 are of such length that, when assembled with plate 42 and the other ladder components, and when in a neutral or equalized condition, the overall length of the rear legs is substantially equal to that of front legs 12 and 14.

Accordingly, it is apparent that said leg extensions 32 and 34- are free to be manually shifted relative to each other and to the rear prop legs within which they are housed, in order to effect a longer or shorter extension of one or the other leg as required by the terrain or supporting surface on which it is used.

The novel means for locking the adjustable legs in their selected positions include a shiftable locking detent or dog 48 which is engageable between adjacent pairs of a plurality of teeth 50 provided on the upper or central portion of the arcuate periphery of the equalizing plate 42. More specifically, the locking detent 48, which is mounted for freely shiftable movement along the underside of the top platform 18 perpendicularly to the plane of plate 42, preferably comprises a main body of T-shaped cross section having a narrowed or reduced finger 52 at one end of a size to readily fit between adjacent pairs of teeth 50 on the plate 42 The cross arms or wings of the T are disposed horizontally and are slidingly supported within spaced apart guide members 5 5, 54, best seen in FIG. 1, which are preferably secured to the underside of the top platform 18.

The means for actuating the shiftable detent 48, to

' efiect engagement and disengagement of the finger 52 with the teeth 50, include a pair of bell cranks S6, 56 pivotally mounted at 58 in opposed alignment within the upper portions of and to the front legs 12 and 14, and to which is affixed an upwardly bowed interconnecting arm 60 which is adapted to operatively engage in a slot 62 provided in the depending web of the T-shaped body of the detent 48. Offset from the arm 60 and the pivoted mounting 58 of each bell crank 56, there is an operating lever or rod 64 having its upper end pivotally connected at 66 to the bell crank, and extending downwardly and freely through notches 68 (FIG. 1) provided in the steps 16. The rods 64, 64 terminate in and are rigidly affixed to enlarged foot members 70 which are adapted for sliding movement within, and normally extend slightly beyond, the lower extremities 72 of front legs 12 and 14 when the rods 64, 64- and associated elements are not in operative locking condition, as seen better in FIG. 4. FIG. 4 also shows in dotted outline the general displacement of the locking components when moved into locked condition in response to the application of a users weight on the ladder, which causes vertical movement of rods 64, 64 relative to front legs 12 and 14, and in turn effects pivotal movement of the bell cranks 56, 56 and arm 60 and shiftable movement of detent 48, whereby finger 52 engages between teeth 50 and locks the equalizing plate 42 and the rear leg extensions 32, 34 in the positions then occupied.

In order to increase the stability of the ladder, foot members 70 are provided with flexible non-slip coverings or boots 73 which are suitably secured to the bottom portions of the foot members, and telescope over and are slidable relative to the lower extremities 72 of the front legs 12 and 14.

The means for effecting automatic release of the detent finger 52 include a pair of compression springs 74, 74 which are disposed around and secured or fixed at their lower ends to the rods 64, 64 as at 76, in FIG. 4. The springs are so disposed that their upper ends abut the bottom of one of the steps 16, in a manner whereby the springs are compressed when the user steps on the ladder and then expand when he steps off, the expansion resulting in relative movement between the front legs 12 and the rods 64, 64 which effects withdrawal of detent 48 and unlocking or disengagement of finger 52 with the teeth 50. Expansion of the springs 74, 74 also results in upward movement of the lower extremities 72 of legs 12 and 14 relative to the foot portions 70, 70 and their non-slip boots 73.

It is apparent from the foregoing description that an improved safety ladder has been provided which achieves all of the objectives and advantages set forth in the preamble of this specification. While only one specific embodiment of the inventive concept has been illustrated and described in detail, it is to be expressly understood that the drawings are not to be construed as representative of the full scope of the invention as it is defined in the appended claims.

I claim:

1. In combination with a ladder of the class described having interconnected, reciprocably adjustable leg extensions movably housed within a pair of side frame members of said ladder, means responsive to application of the users weight on said ladder for locking said extensions in predetermined positions relative to said side frame members, comprising:

(a) an arcuate shaped equalizing plate pivotally mounted between said ladder side frame members and having a plurality of locking teeth on the arcuate periphery thereof;

(b) said equalizing plate being pivotally connected at opposite sides to the adjustable leg extensions;

(c) a detent finger disposed on said ladder frame and adapted for releasable engagement with said locking teeth;

(d) a pair of hell cranks operably connected to said detent finger and pivotally carried by said ladder frame; and

(e) means responsive to application of the users weight on said ladder for actuating said bell cranks.

2. The combination as defined in claim 1, wherein:

(a) the side frame members serve as a pair of rear prop legs;

(b) the ladder further includes a pair of front legs having steps therebetween;

(c) and the means for actuating said bell cranks include:

(1) a pair of foot members respectively disposed adjacent the lower ends of the front legs and adapted for engagement with the supporting surface on which the ladder is to be used; and

(2) a pair of actuating rods respectively interconnecting the actuating feet and the bell cranks.

3. The combination as defined in claim 2, wherein the means for actuating said bell cranks further include means responsive to withdrawal of the users weight from said ladder for automatically releasing the locking components, comprising yieldable means adapted to be placed under compression by the users weight during use of the ladder and to expand and return the locking components to an unlocked condition when the ladder is not in use.

4. An adjustable safety ladder of the class described comprising:

(a) a pair of front leg guide members and a pair of rear leg guide members connected to an upper portion of the ladder;

(b) said rear leg members being shorter than said front leg members;

(0) an equalizing semicircular mounting plate pivotally disposed between said rear leg members near the upper portion of said ladder, and having a plurality of teeth formed in the midportion of the semicircular periphery of said plate;

((1) a pair of leg extensions guidably disposed within,

and having the lower ends thereof projecting a substantial distance below, the rear legs, the upper ends of said leg extensions being pivotally connected to opposite sides of said equalizing plate, whereby said leg extensions are adapted for shiftable movement relative to each other and to the rear leg members; and

(e) releasable locking means responsible to the application of a users weight upon the ladder for locking said leg extensions in a given predetermined position;

(f) said locking means including:

(1) a slidable detent carried by said upper portion of the ladder for engagement with said teeth on the equalizing plate;

(2) a bell crank pivotally mounted on one of said front leg members and operably connected with said detent;

(3) a foot member slidably disposed within and adjacent the lower end of one of the front leg members and adapted for engagement with the supporting surface on which the latter is to be used; and

(4) an actuating rod interconnecting said foot member and bell crank.

5. An adjustable leg safety ladder of the class described comprising:

(a) a ladder frame including a pair of rear legs, a pair of front legs and a plurality of steps affixed to said front legs;

(b) said rear legs being shorter than said front legs and having adjustable leg extensions associated therewith and operatively interconnected with one another;

(c) a lockable equalizing plate pivotally mounted on said ladder frame between said rear legs, including an arcuate toothed peripheral portion;

(d) said extension legs being pivotally connected at their upper ends to opposite sides of said equalizing plate for reciprocable shiftable movement relative to each other and to said rear legs; and

(e) locking means carried by said ladder frame and engageable with said equalizing plate for releasably locking said extension legs in a predetermined shifted condition, said locking means including:

(1) a locking detent disposed for operable engagement with the toothed portion of said equalizing plates;

(2) a bell crank lever pivotally mounted on one of said ladder legs and operably connected with said detent;

(3) means responsive to the application of weight to the ladder frame of actuating said bell crank lever to effect engagement of said detent with said plate; and

(4) resilient means operably disposed between said frame for actuating the bell crank lever and the ladder frame.

6. An adjustable leg safety ladder of the class described comprising:

(a) a ladder frame including a pair of rear legs, a pair of front legs and a plurality of steps affixed to said front legs;

(b) said rear legs being shorter than said front legs and having adjustable leg extensions associated therewith and operably interconnected with one another;

(c) a lockable equalizing plate pivotally mounted on said ladder frame between said rear legs, including an arcuate toothed peripheral portion;

((1) said extension legs being pivotally connected at their upper ends to opposite sides of said equalizing plate for reciprocable shiftable movement relative to each other and to said rear legs; and

(e) locking means carried by said ladder frame and engageable with said equalizing plate for releasably locking said extension legs in a predetermined shifted condition, said locking means including:

(1) a locking detent disposed for operable engagement with the toothed portion of said equalizing plate;

(2) a bell crank lever pivotally mounted on one of said ladder legs and operably connected with said detent; and

(3) means responsive to the application of weight to the ladder frame for actuating said bell crank lever to effect engagement of said detent with said plate including:

(A) a foot member slidable with respect to the lower end of one of said front legs adapted for engagement with the supporting surface on which the ladder is to be used; and

(B) an actuating rod interconnecting said foot member and said bell crank lever.

7. The combination as defined in claim 6 wherein the locking means include a spring having one end affixed to said actuating rod and the other end adapted to bear against a portion of the ladder frame, said spring being compressible to permit relative movement of said locking components when weight is applied to the ladder frame and expanding to automatically disengage said locking components when the weight is withdrawn from the ladder frame.

References Cited by the Examiner UNITED STATES PATENTS 983,172 1/1911 Sheetz 182-200 1,401,354 12/1821 Niccum 182200 X 1,516,988 11/1924 Redman 182202 2,476,650 7/ 1949 Biery 182-202 2,854,180 9/1958 Brunckhorst 182202 HARRISON R. MOSELEY, Primary Examiner.

REINALDO P. MACHADO, Examiner. 

1. IN COMBINATION WITH A LADDER OF THE CLASS DESCRIBED HAVING INTERCONNECTED, RECIPROCABLY ADJUSTABLE LEG EXTENSIONS MOVABLY HOUSED WITHIN A PAIR OF SIDE FRAME MEMBERS OF SAID LADDER, MEANS RESPONSIVE TO APPLICATION OF THE USER''S WEIGHT OF SAID LADDER FOR LOCKING SAID EXTENSIONS IN PREDETERMINED POSITIONS RELATIVE TO SAID SIDE FRAME MEMBERS, COMPRISING: (A) AN ARCUATE SHAPED EQUALIZING PLATE PIVOTALLY MOUNTED BETWEEN SAID LADDER SIDE FRAME MEMBERS AND HAVING A PLURALITY OF LOCKING TEETH ON THE ARCUATE PERIPHERY THEREOF; (B) SAID EQUALIZING PLATE BEING PIVOTALLY CONNECTED AT OPPOSITE SIDES TO THE ADJUSTABLE LEG EXTENSIONS; (C) A DETENT FINGER DISPOSED ON SAID LADDER FRAME AND ADAPTED FOR RELEASABLE ENGAGEMENT WITH SAID LOCKING TEETH; (D) A PAIR OF BELL CRANKS OPERABLY CONNECTED TO SAID DETENT FINGER AND PIVOTALLY CARRIED BY SAID LATTER FRAME; AND (E) MEANS RESPONSIVE TO APPLICATION OF THE USER''S WEIGHT ON SAID LADDER FOR ACTUATING SAID BELL CRANK. 